Lately, broadcasting by way of broadcast satellites and communication satellites and, even in terrestrial broadcasting, so-called digital TV broadcasting are growing popular in addition to traditional analog TV broadcasting. At home, systems for receiving different types of broadcasting are coming into popular use. In these digital systems, a huge number of programs are broadcasted, because many more channels are available than are provided in the traditional analog broadcasting only. Meanwhile, to record and play back such a great number of broadcast programs, diverse types of AV devices such as digital video tape recorders (VTRs), disk recorders, etc. are being put on the market one after another.
By the way, because recording/playback devices, such as digital VTRs perform digital recording and playback of video and audio signals, these devices inherently keep the signal quality free from deterioration. However, this means that same quality copies of originals can easily be made, and a possibility of unauthorized copying of a copyright program is pointed out. To eliminate this problem, e.g., a Digital Transmission Contents Protection (DTCP) scheme has lately been adopted for 1394 buses as a technique for preventing unauthorized copies. In this DTCP scheme, copy control information describing conditions for copying is added to audio and video streams, and the following three categories are defined: “copy free” (no limitation on copying), “copy never” (copying is prohibited), and “copy one generation” (copiable but once only). In the meantime, the recording/playback devices, such as digital VTRs are allowed to receive and record streams of “copy free” or “copy one generation” solely among the above categories. If a device records a “copy one generation” stream, it must change the copy control information in the recorded signal stream to “no more copies” (uncopiable) so that the stream is prohibited from being recorded any more by another recording device.
Recently, a stream recording/playback device called an HDD recorder has been realized. This device incorporates a large-capacity information recording medium, such as a hard disk drive (HDD) and, therefore, receives a great number of channels and records video and audio stream data on the HDD. However, the capacity of the disk fixedly installed in the device is still capped, even for the HDD recorder. Thus, if free disk space becomes scarce, the user would have to transfer content that is video and audio stream data stored on the disk to an external device, such as a VTR and an optical disk drive and store the content on another storage medium such as a magnetic tape or an optical disk on which information can be recorded.
In view of this situation, the above DTCP scheme defines a so-called “MOVE” function that enables moving of content by copying “no more copies” content once recorded on a recording medium to another recording medium and then deleting the original content or making it unable to be played back. According to the move function, this function can be executed solely for one recording medium, e.g., the one that is included in a receiver or digitally connected to the receiver, and it is stated that reproducible content data streams longer than one minute (60 seconds) must not exist on both the move source and the move destination simultaneously. A technique for implementing the move function is already known, e.g., the technique described in published patent application document (US2002/0114462A1).
Because of the need to delete or disable source content, to limit overlap on the two devices to less than 60 seconds, content may be damaged or lost due to an interruption of the move process, e.g., due to loss of power. A technique using the move function that can cope with a situation where the power of the source or destination device is tuned off in the course of moving content is already known, e.g., in patent documents (US2002/0114462A1, US2002/0141580A1). In this technique, a file recorded on the source recording medium is segmented into smaller data of a predetermined size and the data is transferred to the receiving side device. Each time such data is output, the data is erased from the source recording medium. In case the sending side device or the receiving side device is powered off in the course of data output operation, an end flag is added to the data that is output to the receiving side device.